Various techniques have been developed to fabricate a display device with a display cover bonded to a display panel. In one conventional technique, the display cover is bonded to a perimeter of the display panel using an adhesive material, while leaving an air gap between the display cover and the display panel. With this design, the air gap between the display cover and the display panel significantly reduces the optical performance of the display device due to the refractive index mismatch at the interface between the display cover and the air gap. For example, a display cover made of glass has an index of refraction of about 1.5, wherein air has an index of refraction of about 1.0. This mismatch in the refractive index results in increased parasitic reflections at the interface between the display cover and air gap, which reduces the display contrast ratio and, thus degrades viewability. In addition, condensation can form in the air gap between the display panel and the display cover, which can further degrade the optical performance of the display device.
Other conventional techniques include liquid bonding and dry film bonding techniques, which serve to eliminate the air gap by bonding a display cover to a display panel using a bonding material that has a refractive index which is matched to the display cover. For example, with liquid bonding techniques, a liquid adhesive material such as epoxy, silicon or urethane, is applied between the display panel and the display cover. The liquid adhesive material is then cured/hardened through UV (ultraviolet light), heat, moisture, or a combination thereof (depending on the type of liquid adhesive material used) to bond the display cover and the display panel together. Furthermore, dry bonding techniques generally include the use of a non-liquid optical tape, or disposing a thin laminate sheet of optical material (e.g., optical thermoplastic material) between the display panel and the display cover and applying a suitable temperature and pressure which causes the thin laminate sheet of optical material to adhere to the display panel and display cover.
While liquid and dry bonding techniques improve optical performance of the display device by replacing the air gap with a material having a matching refractive index, the optical performance of display devices constructed using such techniques can degrade over time as a result of delamination at the interfaces of the bonded components. Indeed, a delamination can occur as a result of mechanical stresses that are applied at the interfaces between the different bonded components. These mechanical stress can result from repeated shock or vibration applied to the display device, or shear stresses that are applied at the interfaces between the bonded components of the display device due to different rates of thermal expansion of the different materials of the bonded components. In addition, delamination can result due to uneven mounting pressure, altitude or other environmental or mechanical issues. The delamination at the interface(s) of the bonded components can cause significant visual anomalies and luminance irregularities of the display device, thereby degrading the optical performance of the display device.